collision detection

[benjamin]

Hello,
I am putting together a simple game using ascii characters and while I have movement, and limiting the area of movement down pat, I became stumped when I thought about putting in buildings and how I would go about coming to a halt when I hit them, rather than going through them. Here is a snippet of code in its simplest form. I am putting a simple building in as the first line of code so it is easier to spot and have numbered the movement lines for simplicity sake:

'building
LOCATE 13, 32: COLOR 4, 0: PRINT STRING$(5, 219)
'movement
100 PX = 7: PY = 22
LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64)
101 K$ = INKEY$
102 K$ = RIGHT$(INKEY$, 1): IF K$ = "" THEN GOTO 102
IF K$ = "2" OR K$ = "P" THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250); : PX = PX + 2: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64)
IF K$ = "8" OR K$ = "H" THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250); : PX = PX - 2: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64)
IF K$ = "4" OR K$ = "K" THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250); : PY = PY - 2: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64)
IF K$ = "6" OR K$ = "M" THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250); : PY = PY + 2: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64)
IF PX > 39 THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250): PX = 39: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64): GOTO 101
IF PX < 7 THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250): PX = 7: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64): GOTO 101
IF PY > 77 THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250): PY = 77: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64): GOTO 101
IF PY < 22 THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250): PY = 22: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64): GOTO 101
IF K$ = CHR$(27) THEN CLS : END
GOSUB 101

What couuld I add to this in order to stop the character from walking through the building? Thank you in advance for any assistance with this.

[Guest]

Code: Select all

psuedo: IF playerX < builingX then movechararcter

[benjamin]

<scratches head>
I guess I don't understand that code.

[Rattrapmax6]

Basicaly, you set it so when character's X, Y equals the Building's wall X, Y the program stops motion in that direction. Normaly to stop, you reverse the number of steps the character took b4 hitting the wall.

Code: Select all

PlayX = PlayX + 1

IF PlayX = BuildX THEN PlayX = PlayX - 1

/\ In it's simplist form....

[{Nathan}]

Ratt, that works, but I find this to be more efficiant (smaller and faster)

Code: Select all

IF PlayerX + 1 < TheThingUdontWannaHitX THEN PlayerX = PlayerX + 1

Really, I find that just small things (like defining consts Left = 1, ect) is better so instead of that, I would use this. I know its bigger, but it looks WAY better. QB just needs inline subs...

Code: Select all

CONST Left = 1, Right = 2, Up = 3, Down = 4
...
IF Player.X > CollisionThing.X THEN MovePlayer(Left)

SUB MovePlayer(Dir as integer)
'its obvious what goes here! duh...[code]

[benjamin]

Ahhh, okay, I got it. Thanks guys.

[matt2jones]

You could also use the SCREEN function to check what character is infront of the @, and if it's a wall, don't allow them the @ to move.

It's not good programming practice to do collisions straight from the screen like that, but if you have allot of walls it's easier to manage.

Code: Select all

IF K$ = "2" OR K$ = "P" and SCREEN(PX+2,PY) <> [i]*WALL*[/i] THEN LOCATE PX, PY, 0: COLOR 8, 0: PRINT CHR$(250); : PX = PX + 2: LOCATE PX, PY, 0: COLOR 7, 0: PRINT CHR$(64) 

matt